The present invention relates to an airfoil for a bucket of a stage of a gas turbine and particularly relates to a stage one bucket airfoil having an optimized number, location, style and size of perimetrically-arranged cooling holes for flowing a cooling medium, e.g., air, through the airfoil.
There are many different types and numbers of passages for flowing a cooling medium through an airfoil for cooling the airfoil. While the different cooling mediums may be used, many airfoils are air-cooled, It will be appreciated that the air used to cool gas turbine airfoils of this type is derived from the compressor and therefore results in a debit to the overall efficiency of the turbine. A prior cooling configuration for a bucket of a particular turbine did not sufficiently cool the bucket. Problems were associated with bulk creep and oxidation and a more effective cooling scheme which decreases the bulk temperature of the bucket and increases both the bucket's bulk creep life and oxidation life was deemed necessary. A further prior perimeter-cooled stage one bucket utilizes a perimeter cooling scheme. However, in the present turbine, this prior air-cooled bucket could not be utilized as it is not a direct scale regarding the size, location, style and number of cooling holes through the airfoil. Accordingly, there is a need to provide an optimized cooling scheme for a particular airfoil of a turbine bucket which utilizes a minimum amount of the cooling medium, e.g., air, and, hence, an increase in efficiency of the turbine, as well as a cooling scheme which will increase both bulk creep and oxidation life.